Mobile device battery



FIG. 1 is a front view of a mobile device battery showing our new design;

FIG. 2 is a side view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof; and,

FIG. 5 is a back view thereof.

The broken lines shown in FIGS. 1-5 are included for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a mobile device battery, as shown and described. 